Fluorinated analogs of norepinephrine, isoproterenol, phenylephrine, tyramine, dopamine, melatonin, serotonin, DOPA, and alpha-methylDOPA have been synthesized. Biochemical and biophysical studies on these analogs have revealed important information concerning conformational requirements for norepinephrine in interaction with alpha and beta-adrenergic receptors, and the role of phenolic pK and lipophilicity in determining activity of biogenic amines. The use of 19F NMR spectroscopy as a probe for molecular motion has revealed important information concerning the mechanism of serotonin storage in human platelets.